The present invention relates to earth retaining walls. More particularly, the present invention relates to mechanically stabilized earth retaining walls secured by backfill loading to laterally extending soil reinforcement sheets independently of normal stress imposed by the mass of the blocks defining the wall.
Mechanically stabilized earth retaining walls are construction devices used to reinforce earthen slopes, particularly where changes in elevations occur rapidly, for example, site developments with steeply rising embankments. These embankments must be secured, such as by retaining walls, against collapse or failure to protect persons and property from possible injury or damage caused by the slippage or sliding of the earthen slope.
Many designs for earth retaining walls exist today. Wall designs must account for lateral earth and water pressures, the weight of the wall, temperature and shrinkage effects, and earthquake loads. The design type known as mechanically stabilized earth retaining walls employ either metallic or polymeric tensile reinforcements in the soil mass. The tensile reinforcements extend laterally of the wall formed of a plurality of modular facing units, typically precast concrete members, blocks, or panels, stacked together. The tensile reinforcements connect the soil mass to the blocks that define the wall. The blocks create a visual vertical facing for the reinforced soil mass.
The polymeric tensile reinforcements typically used are elongated lattice-like structures often referred to as grids. These are stiff polymeric extrusions. The grids have elongated ribs which connect to transversely aligned bars thereby forming elongated apertures between the ribs.
Various connection methods are used during construction of earth retaining walls to interlock the blocks or panels with the grids. One known type of retaining wall has blocks with bores extending inwardly within the top and bottom surfaces. The bores receive dowels or pins. After a first tier of blocks has been positioned laterally along the length of the wall, the dowels are inserted into the bores of the upper surfaces of the blocks. Edge portions of the grids are placed on the tier of blocks so that each of the dowels extends through a respective one of the apertures. This connects the wall to the grid. The grid extends laterally from the blocks and is covered with back fill. A second tier of blocks is positioned with the upwardly extending dowels fitting within bores of the bottom surfaces of the blocks. The loading of backfill over the grids is distributed at the dowel-to-grid connection points. The strength of the grid-to-wall connection is generated by friction between the upper and lower block surfaces and the grid and by the linkage between the aggregate trapped by the wall and the apertures of the grid. The magnitude of these two contributing factors varies with the workmanship of the wall, normal stresses applied by the weight of the blocks above the connection, and by the quality and size of the aggregate.
Other connection devices are known. For example, my U.S. Pat. No. 5,417,523 describes a connector bar with spaced-apart keys that engage apertures in the grid that extends laterally from the wall. The connector bars are received in channels defined in the upper and lower surfaces of the blocks.
The specifications for earth retaining walls are based upon the strength of the interlocking components and the load created by the backfill. Once the desired wall height and type of ground conditions are known, the number of grids, the vertical spacing between adjacent grids, and lateral positioning of the grids is determined, dependent upon the load capacity of the interlocking components.
Heretofore, construction of such mechanically stabilized earth retaining walls has been limited to large, financially significant projects. This is due in part to the cost of the mechanical components used for construction of such earth retaining walls. To reduce costs, tensile reinforcements other than grids have been developed for use with mechanically stabilized earth retaining walls. These other tensile reinforcements are flexible reinforcement sheets, including large open grid woven lattices and small aperture woven lattices, as well as woven textile sheets. These other tensile reinforcements are significantly less expensive than extruded grids. However, when these other flexible reinforcements are used in construction of mechanically stabilized earth walls, their connection with the wall facing units has been a major technical challenge. Up to now, the flexible reinforcements are connected to the modular blocks through the block/reinforcement friction. The magnitude of the frictional force, (i.e., connection strength) depends on the overburden pressure acting on the particular reinforcement sheet under consideration. The higher the overburden pressure, the larger the connection strength. For small walls, the normal stresses that are applied by the weight of blocks are limited and the required connection strength is often difficult to meet.
Accordingly, there is a need in the art for an earth retaining wall that is stabilized independently of the normal stress imposed by the mass of the blocks in the wall. It is to such that the present invention is directed.
The present invention meets the need in the art by providing an earth retaining wall that comprises at least two stacked tiers of blocks placed side by side. Each of the blocks defines a channel extending between opposing sides with the channel defining at least two adjacent bearing surfaces and an opening between the bearing surfaces to a slot extending laterally from the channel to an exterior side of the block. An elongate clamping bar conforming in cross-sectional shape at least relative to the pair of adjacent bearing surfaces defined in the channel, is received within the channel with an apex thereof adjacent the opening of the channel to the slot and with a portion of a reinforcement sheet wrapped around the clamping bar and the reinforcement sheet extending through the slot laterally of the tiers of blocks. The clamping bar mechanically engages the bearing surfaces of the channel such that the tensile loading carried by the reinforcement sheet is distributed across the bearing surfaces of the block.
In another aspect, the present invention provides a method of constructing an earth retaining wall, comprising the steps of:
(a) placing at least two stacked tiers of blocks side by side to define a length of a wall, each of the blocks defining a channel extending between opposing sides thereof, the channel defining at least two adjacent bearing surfaces and an opening between the bearing surfaces to a slot extending from the channel to an exterior side of the block;
(b) wrapping an edge portion of a reinforcement sheet over a clamping bar conforming in cross-sectional shape at least relative to the pair of adjacent bearing surfaces defined in the channel;
(c) sliding the wrapped clamping bar with the reinforcement sheet along the channel with a laterally extending portion of the reinforcement sheet slidingly received within the slot and extending the reinforcement sheet laterally of the wall, an apex of the clamping bar aligned with the opening of the channel to the slot; and
(d) covering the portion of the reinforcement sheet lateral of the wall with backfill,
whereby the clamping bar, being wrapped by the reinforcement sheet that is loaded by backfill covering the laterally extending portion of the reinforcement sheet, mechanically engages the two bearing surfaces of the channel such that the tensile loading is distributed across the block.
In another aspect, the present invention provides a connector for engaging a reinforcement sheet extending laterally of an earth retaining wall formed of tiers of side-by-side blocks which each block defines a channel extending from one side of the block to an opposing side, the channel defining at least two adjacent bearing surfaces and opening between the bearing surfaces to a slot that extends from the channel to an exterior face of the block for receiving therein a portion of the reinforcement sheet. The connector therefor comprises an elongate member conforming in cross-sectional shape at least relative to the pair of adjacent bearing surfaces defined in the channel extending through the block. The elongate member, being enwrapped with a portion of the reinforcement sheet that extends through the slot laterally of the block and covered by backfill, communicates the tensile loading from the reinforcement sheet to the block by bearing portions of the member against the bearing surfaces of the channel.
In another aspect, the present invention provides a block for constructing an earth retaining wall formed of a plurality of the blocks placed side-by-side in tiers, in which the block comprises a body defined by two opposing sides, a top and an opposing bottom, and a front face and an opposing back face, the body defining a channel that extends between the opposing sides for receiving a clamping bar therein with the channel defining at least two adjacent bearing surfaces for engaging surfaces of the clamping bar and an opening between the bearing surfaces to a slot that extends from the channel to an exterior face of the block for receiving therein a portion of a reinforcement sheet. The clamping bar, being wrapped with a portion of the reinforcement sheet that extends laterally of the block through the slot and being received within the channel, bears against the bearing surfaces to transfer tensile loading from the reinforcement sheet to the block.
Objects, advantages and features of the present invention will become apparent from a reading of the following detailed description of the invention and claims in view of the appended drawings.